List which modules selfupdate
would upgrade. You can update either
the core (CPANPLUS itself), the core dependencies, all features you have
currently turned on, or all features available, or everything.

The latest
option determines whether it should update to the latest
version on CPAN, or if the minimal required version for CPANPLUS is
good enough.

Returns a hash of feature names and lists of module objects to be
upgraded based on the category you provided. For example: